The present invention relates to an improvement in means for shifting gears on dual shift bicycles, i.e., bicycles having two sets of sprocket clusters and means for shifting the drive chain between the sprockets thereof. Such bicycles generally are designed to operate at various gear ratios (speeds), such as 10, 12, 15 etc.
The present day dual shift bicycles have two shift handles, one for each of the front and rear derailleur mechanisms, and are cumbersome and difficult to operate. The two handles are interactive and must be manipulated in a manner that is beyond the knowledge and skill of the average operator (bike rider). The bike rider must operate either or both of the gear selection handles in order to shift the bicycle to the desired gear ratio. The two handles must be adjusted further after the shift is completed, such further adjustment generally being made by ear while listening for rubbing and/or grinding of the drive chain. It is extremely difficult for the operator to remember which handle or handles are to be operated to place the gear shift in the desired one of the ten different gear ratios and the operator must also consider whether he is shifting up or down and remember which gear he is in prior to the shifting operation.
Various attempts have been made to overcome the above-discussed problems in the dual shift bicycles in general use today. For example, U.S. Pat. Nos. 4,055,093; 3,965,763; and 3,901,095 disclose attempts at overcoming the above-described problems. U.S. Pat. No. 4,055,093 discloses a control for a ten speed bicycle comprising a single manually movable control member associated with a pair of cams for actuating the front and rear derailleurs. U.S. Pat. Nos. 3,965,763 and 3,901,095 disclose gear shifts for dual shift bicycles in which a single continuous cable is actuated to control cams which actuate the front and rear derailleurs. Prior art U.S. Pat. No. 3,121,575 is also acknowledged.
The above-described prior art patents do not provide a practical solution to the problems of the present day dual shift bicycles in use. The device disclosed in U.S. Pat. No. 4,055,093, for example, requires the shifting back and forth of the derailleurs for intermediate gears with the mechanism going sequentially through each gear each time a gear shift is made.
In accordance with the present invention there is provided a control means for shifting gears on dual shift bicycles that is easy to operate and applicable for the shifting of gears on all dual shift bicycles. The control means of the present invention is constructed so that the front and rear derailleurs are controlled together to shift to any selected gear from any engaged gear with a single operator action. Accordingly, the operator need not concern himself with which one or both of the derailleurs is to be shifted, which direction to shift the derailleurs, or how much the derailleurs are to be shifted.
In accordance with the invention there is provided a pre-select feature that allows the operator to anticipate and select the next gear change while continuously pedaling in the present gear. The actual gear change can be postponed by the operator indefinitely or can be overridden by a different subsequent selection if desired.
Furthermore, the control means of the present invention operates to directly position both front and rear derailleurs for the selected gear without any back and forth shifting for intermediate gears. This allows for the fastest possible shift between any two gears. A feature of the control means in accordance with the invention is that shifting can take place with both hands of the operator (bicycle rider) on the handle bars to provide increased safety and better control.
Furthermore, the control means is designed so that when shifting between two gears that engage the same sprocket of the sprocket cluster associated with the front derailleur (ie., either the large or small sprocket), the mechanism is precisely positioned to avoid the occurrence of rubbing as a result of a new rear sprocket selection.
Also, the selection and control means are designed to facilitate a rapid series of up shifts or down shifts. (Rapid down shifting, for example, as needed for efficient hill climbing.) Such a series of up shifts or down shifts can be made without intervening gear selections between shifts.
In the achievement of the above-described ends, the mechanism of the present invention will indicate the gear presently engaged or preselected by the operator, ie., gear ratios (speeds) 1-10 for a ten speed bicycle, and provide for simple, error free shifting into any selected higher or lower gear. The bicycle rider need not be concerned with calculating or memorizing any shifting sequence.